Testing Controls

Network I/O control prioritizes network traffic by type when
using network resource pools and the native VMware vNetwork Distributed Switch.
Network I/O control only works with Version 4.1 of the vNetwork Distributed
Switch; not Cisco Nexxus V1000 and not the standard switch from VMware. IT
managers who are already using the vNetwork Distributed Switch will need to
upgrade to Version 4.1.
While it takes advanced network expertise to design and tune
the policy that runs network I/O controls, the actual implementation of the
feature is quite simple. Entering the parameter changes to enable the feature
and set the specific physical network adapter shares is just a matter of
walking through a couple of configuration screens that are easily accessed from
the vSphere client. I was able to assign low, medium, normal, high or a custom
setting that designated the number of network shares-a policy designation that
represents the relative importance of virtual machines that are using the same
shared resources-that would be allocated to VM, management and fault-tolerant
traffic flows.

Storage I/O controls were equally easy to configure once the
policy decisions and physical prerequisites were met. In my relatively modest
test environment it was no trouble to run storage I/O controls on a single
vCenter Server. I tested this feature on an iSCSI-connected storage array. It
also works on Fibre Channel-connected storage, but not NFS
(Network File System) or Raw Device Mapping storage. There are other
requirements and restrictions that make this feature one more suited for
evaluation for strategic implementation, including tiered storage system
certifications.

Virtual machines can be limited based on IOPS (I/O
operations per second) or megabytes per second. In either case, I used storage
I/O controls to limit some virtual machines in order to give others priority. I
found the large number of considerations-for example, each virtual disk
associated with each VM must be placed under control for the limit to be
enforced-meant that I spent a great deal of time figuring out policies to get a
modest amount of benefit when my systems were actually running.
Memory
VMware included a handy memory innovation in vSphere 4.1
called "memory compression." IT managers would do well to become
familiar with the feature, as it is enabled by default. In my tests I saw
improvements in virtual machine performance after I artificially constrained
the amount of physical host memory. As my VM systems started to access memory
to handle test workloads, my ESX 4.1 system started to compress virtual memory
pages and store them to a compressed memory cache.
Since accessing this memory is significantly faster than
swapping memory pages to disk, the virtual machines ran much faster than when
this feature was disabled and the same workloads were started. System and
application managers will likely need to work together to work out the best
formula for utilizing memory compression. I made extensive use of the memory
performance metrics to see what was happening to my test systems as I
constrained the amount of host memory. IT managers should expect to devote at
least several weeks of expert analysis to determining the most effective memory
compression configuration for each workload.
Housekeeping
In addition to the changes made in handling system
resources, VMware did some housekeeping in the incremental release of vSphere.
The vSphere client is still available in the vCenter 4.1 installation bits but
is no longer included in the ESX and ESXi code. Instead, users are directed to
a VMware Website to get the management client. There were some minor changes
made to various interface screens, but nothing that will puzzle an experienced
IT administrator.

Cameron Sturdevant has been with the Labs since 1997, and before that paid his IT management dues at a software publishing firm working with several Fortune 100 companies. Cameron also spent two years with a database development firm, integrating applications with mainframe legacy programs. Cameron's areas of expertise include virtual and physical IT infrastructure, cloud computing, enterprise networking and mobility, with a focus on Android in the enterprise. In addition to reviews, Cameron has covered monolithic enterprise management systems throughout their lifecycles, providing the eWEEK reader with all-important history and context. Cameron takes special care in cultivating his IT manager contacts, to ensure that his reviews and analysis are grounded in real-world concern. Cameron is a regular speaker at Ziff-Davis Enterprise online and face-to-face events. Follow Cameron on Twitter at csturdevant, or reach him by email at csturdevant@eweek.com.